Re: ARM CE: CTS IV handling

[Stephan Mueller <smueller@chronox.de>]

Am Dienstag, 19. Mai 2020, 18:21:01 CEST schrieb Ard Biesheuvel:

Hi Ard,

> 
> To be honest, this looks like the API is being used incorrectly. Is
> this a similar issue to the one Herbert spotted recently with the CTR
> code?
> 
> When you say 'leaving the TFM untouched' do you mean the skcipher
> request? The TFM should not retain any per-request state in the first
> place.
> 
> The skcipher request struct is not meant to retain any state either -
> the API simply does not support incremental encryption if the input is
> not a multiple of the chunksize.
> 
> Could you give some sample code on how you are using the API in this case?

What I am doing technically is to allocate a new tfm and request at the 
beginning and then reuse the TFM and request. In that sense, I think I violate 
that constraint.

But in order to implement such repetition, I can surely clear / allocate a new 
TFM. But in order to get that right, I need the resulting IV after the cipher 
operation.

This IV that I get after the cipher operation completes is different between C 
and CE.

Ciao
Stephan